This invention relates to magnetization detectors for magnetic cores. Specifically, the invention is an apparatus and method for qualitatively detecting the absence or presence of residual magnetic fields in matched pairs of magnet cores.
In many instrumentation applications, particularly various high energy physics experiments which use electro magnet fields to steer charged particles it is desirable to be able to measure the condition of electro magnet cores used in the experiment to detemine whether or not there are residual fields in the magnetic cores left over from a previous excitation which might distort or disturb calibration of other test equipment used to evaluate experimental results. In particular, it has been found important in various experiments at the Fermi Lab Accelerator to be able to determine the state of magnetic cores prior to the conducting of an experiment. At Fermi Lab, a 110 foot long muon pipe comprised of 220 individual tape wound steel toroids is used to deflect unwanted halo muons in certain types of high energy physics experiments. Tests need to be conducted with and without the magnetic field provided by the assembly of magnet cores. A degausing current is passed through the coil windings to reduce the magnetic field to zero before an experiment is run.
Degausing a magnetized core typically requries the application of an alternating excitation current which is gradually decreased to zero amplitude. This process removes the existing remnant magnetic field from the core.
Since the process of degausing requires the application of a decreasing alternating current to the core it is possible to have residual fields left over from the degausing process itself, or previous excitation. It is desirable to be able to detect the presence of any remnant magnetic field left over from the degausing process itself, or not completely removed by the degausing process.
Remnant magnetic field detectors used to detect the presence of magnetic fields in cores are not new and were probably most widely used in computer memory devices, the direction of the residual magnetic field in the cores arbitrarilly being chosen to represent either a binary one or zero. The magnetic core memory is usually "read" by pumping an electric current through a driving coil wrapped around the magnet core. The electric current passing through the driving coil flows in some predetermined direction and induces a directional magnetic field in the core. A sense coil winding also wrapped around the magnet core has a voltage induced in it by magnetic flux changes in the magnet core.
If a current pulse through the driving coil causes a magnetic flux direction change in the core, a voltage pulse is detected at the sense coil in response to the current pulse through driving coil if the residual flux in the core is opposite the direction of the flux generated by the driving coil. If the current pulse through the driving coil did not cause a flux reversal in the core, no flux change is created hence, no output voltage is generated at the sense coil winding.
In the muon pipe described above, wherein individual identical cores must be degaussd and the state of the cores after degausing must determine that it is practically impossible to disassemble and reassemble an assembly of 220 individual cores in any efficient manner. Using individual sense windings on each magnet core would also be prohibitively complex. It is desirable to be able to detect remnant magnetic fields in a typical magnet core or cores, which represents the muon pipe without having to disassemble the muon pipe.
Accordingly, it is therefore an object of the present invention to provide a means to detect remnant magnetic fields in magnetic cores.
It is therefore another object of the present invention to provide a means for detecting remnant magnetic fields in matched magnet core pairs.
Another object of the invention is to provide a means for remotely sensing the existance of remnant fields in matched magnetic core pairs.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combination particularly pointed out in the appended claims.